Piezoelectric materials, in particular PZT (lead-zirconate-titanate), are used in the technology of non-volatile memory devices (FeRAM) and also as actuator and sensor materials in micromechanics.
Although not limited to this, the present invention and the underlying problem will be explained on the basis of PZT.
FIG. 5 shows a schematic cross-sectional presentation of an exemplary piezoelectric PZT layer arrangement as is known from U.S. Pat. No. 7,164,179 B2.
In FIG. 5, reference numeral 1 designates a semiconductor substrate, for example a silicon semiconductor substrate. A layer stack made up of an adhesion/barrier layer 2a, a lower electrode layer 2b, and an optional seed layer 2c, collectively designated with reference numeral 2, is applied to the upper side OS of semiconductor substrate 1. This layer stack 2, and a PZT layer 40 positioned thereabove with an upper electrode 5, are deposited across the entire surface on semiconductor substrate 1 and are structured with the aid of photolithography and subsequent etching processes.
A typical height h1 of layer stack 2 is 50 nm to 500 nm (nanometers), a typical height h2 of PZT layer 40 is 1 μm to 5 μm (micrometers), and a typical height h3 of upper electrode 5 is 50 nm to 400 nm (nanometers).
By using PZT thin-layer multi-stacks in the area of mechanical actuators, it is possible to increase the mechanical deflection at lower operating voltages. When used as sensor material, the sensitivity for the detection of mechanical deformations may be increased in this way.
Layer heights h1, h2, and h3 of the electrodes and additional auxiliary layers required for use as actuator material result in a topography of >1 μm, which prevents integration into modern CMOS processes which depend on planar surfaces. In addition, the manufacture of PZT thin-layer multi-stacks is made more difficult by a topography of this type.